Chloropropyltrimethoxysilane is a key intermediate for the preparation of a variety of amino-, mercapto- and methacryloyloxyorganosilanes, which are used as silane coupling agents (see Deschler, et al., Angewandte Chemie, Int. Ed., Engl., 25 (1986) 236-252). Chloropropyltrimethoxysilane can also be converted into chloropropyltriethoxysilane, a key intermediate for the preparation of poylsulfane-containing organoalkoxysilanes, which are used in the manufacture of silica-filled tires.
U.S. Pat. No. 6,191,297 discloses a two-step process comprising the ethanol esterification of the product obtained from the platinum-catalyzed hydrosilylation of allyl chloride by trichlorosilane. This process is highly inefficient in its use of material and plant resources due to low yields and significant byproduct formation, namely, propyltrichlorosilane.
A potentially more economical route is the direct hydrosilylation reaction of triethoxysilane and allyl chloride. Large variations in product yield are disclosed in the prior art for the Pt-catalyzed process. According to U.S. Pat. No. 3,795,656, and Japanese Patent 11-199588, the Pt-catalyzed hydrosilylation reaction of allyl chloride and triethoxysilane produces a 70% yield of chloropropyltriethoxy-silane. However, Belyakova, et al., (Obshch. Khim., 44 (1974) 2439-2442) report a 14% yield. Chernyshev, et al. (Russ. Chem. Bull. 47(1998) 1374-1378) report a slightly improved yield of 22.7 percent with the use of vinyltriethoxysilane in conjunction with hexachloroplatinic acid.
The primary limitation with the hydrosilylation reaction of allyl chloride and a silane is the competing elimination of propene from allyl chloride. With platinum, the elimination reaction is more prevalent with alkoxysilanes than with chlorosilanes. Rhodium and palladium afford primarily elimination products as depicted in equation (1).H2C═CHCH2Cl→CH3CH═CH2+HCl  (1)
Iridium-containing catalysts have been reported to be very effective for the hydrosilylation reaction of allyl chloride and triethoxysilane. In U.S. Pat. No. 4,658,050, Quirk et al. disclose the iridium-catalyzed hydrosilylation reaction of equimolar quantities of triethoxysilane and allyl chloride with dimeric olefin iridium (I) halide complexes to obtain greater than seventy-five percent yield of 3-chloropropyltriethoxysilane (Cl(CH2)3Si(OC2H5)3). U.S. Pat. No. 5,616,762 illustrates greater than 80 percent yield of this compound, with minimal byproducts, in an iridium-catalyzed hydrosilylation process wherein the allyl chloride is in stoichiometric excess. Japanese Patent Appl. 4 [1992]-225170 reports similar results for the iridium-catalyzed hydrosilylation reaction of allyl chloride and trimethoxysilane.
Ruthenium and its compounds have been reported to be very efficient catalysts for the hydrosilylation reaction of allyl chloride and trialkoxysilanes. Tanaka, et al., (J. Mol. Catal., 81 (1993) 207-214) report the ruthenium carbonyl-catalyzed hydrosilylation reaction of trimethoxysilane and allyl chloride and Japanese Patent Application 8[1996]-261232 discloses the activation of ruthenium carbonyl for use as a hydrosilylation catalyst for the same reaction. Japanese Patent 2,976,011 discloses the Ru-catalyzed hydrosilylation reaction of triethoxysilane and allyl chloride to give chloropropyltriethoxysilane in about 41% yield. U.S. Pat. No. 5,559,264 describes the hydrosilylation reaction of allyl chloride with a stoichiometric excess of hydridomethoxysilane in the presence of a ruthenium catalyst, and preferably in the substantial absence of solvent, to provide chloropropyltrimethoxysilane. U.S. Pat. No. 6,872,845 discloses an improved hydrosilylation process wherein an electron donating aromatic compound is used as a promoter along with the ruthenium-containing catalyst. Both U.S. patents disclose the optional use of 3% O2 in N2 to activate ruthenium-carbonyl and ruthenium-phosphine catalysts for the subject hydrosilylation.
Marciniec, et al. (J. Organomet. Chem., 253 (1983) 349-362) report the use of Ru(II) and Ru(III) phosphine complexes as catalysts for the hydrosilylation of olefins with trialkoxysilanes. A key teaching is the enhancing effect of molecular oxygen on the desired product formation in reactions catalyzed by Ru(II)-phosphine complexes. The authors theorized that the catalytically active species comprised an Ru(III)-phosphine center bonded to a dioxygen (—O—O—) functionality. The publication states (page 356) that conversion of triethoxysilane can sometimes be as high as 75% in the hydrosilylation of allyl chloride and allylamine with RuCl2[(P(C6H5)3]3 and RuCl3[P(C6H5)3]3, but that byproduct formation usually predominates. No information or data was presented on the hydrosilylation of haloalkenes with phosphine-free ruthenium catalysts in the presence of air, oxygen or peroxy compounds.
The beneficial use of molecular oxygen, hydroperoxides and peroxides in some hydrosilylation reactions is known from journal and patent disclosures. Licchelli, et al. (Tet. Lett., 28 (1987) 3719-3722) reported the necessity for benzoyl peroxide in the Pt-catalyzed hydrosilylation of 2-methyl-1-buten-3-yne by methyl dichlorosilane. Alkoxysilanes were not investigated. Benzoyl peroxide usage was 1.64 weight percent of the total weight of reactants. Calhoun, et al., (Trans. Met. Chem., 8(1983) 365-368) found that the catalytic activity of Rh(I)-phosphine complexes for the hydrosilylation of alkenes by alkyl and alkoxysilanes is enhanced by t-butyl hydroperoxide, cumyl hydroperoxide, m-chloroperbenzoic acid, t-butyl perbenzoate and hydrogen peroxide. Optimum product yields depended on the particular combination of metal catalyst and organic peroxy compound. For the hydrosilylation of 1-octene by triethoxysilane, the optimum molar ratio of t-butyl hydroperoxide to Rh was 7.4 for the complex, RhCl(CO)[P(C6H5)3]2. Yields remained approximately constant through molar ratios up to 15.
Calhoun, et al. also investigated the use of Group VIA hexacarbonyls (M(CO)6, M=Cr, Mo, W) in combination with organic peroxides for the hydrosilylation of 2,3-dimethyl-1,3-butadiene by alkyl- and alkoxysilanes. The activities of both Cr(CO)6 and W(CO)6 for formation of the 1-silyl-2,3-dimethyl-2-butene product were enhanced by t-butyl peroxide. Activity of Mo(CO)6 was unaffected by addition of the t-butyl peroxide. Benzoyl peroxide diminished the hydrosilylation activity of Cr(CO)6.
Dickers, et al. (J. Chem. Soc. Dalton (1980) 308-313) investigated the hydrosilylation of propene, hex-1-ene and hex-1-yne with triethylsilane catalyzed by Rh(I) and Ir(I) complexed with cycloalkenyl, phosphine, chloride and carbonyl ligands. Reactions catalyzed with phosphine-containing complexes were inhibited, or did not occur, in the absence of oxygen or t-butyl hydroperoxide. With RhCl[P(C6H5)3]3, optimum rates and product yields occurred at molar ratios of t-butyl hydroperoxide to Rh between 1 and 4. Reduced rates and catalyst deactivation were observed at molar ratios greater than 10. Peroxide or oxygen activation was not necessary with the chloro-bridged, cyclooctenyl dimeric Rh(I) complex, [{RhCl(C8H14)2}2]. IrCl(CO)[P(C6H5)3]2 remained ineffective even with addition of t-butyl hydroperoxide. Di-t-butyl peroxide was completely ineffective in activating RhCl[P(C6H5)3]3. The authors concluded (page 311) that the beneficial effect of oxygen or hydroperoxide was due to the conversion of the phosphine ligands to phoshine oxides, thereby generating a coordinatively unsaturated center with Rh:P molar ratio ˜1. This conclusion also finds support in the data published by Faltynek (Inorg. Chem., 20 (1981) 1357-1362) for photocatalytic hydrosilylations with RhCl[P(C6H5)3]3 in the presence of oxygen and cumeme hydroperoxide.
U.S. Pat. No. 4,578,497 discloses the reactivation of platinum catalysts with oxygen-containing gas to restore hydrosilylation activity with alkyl silanes. The platinum-containing catalyst can be oxygenated prior to use as well as during interruptions in the hydrosilylation process.
U.S. Pat. No. 5,359,113 discloses the use of peroxides and hydroperoxides to maintain catalytic activity in platinum-catalyzed hydrosilylations. Di-t-butyl peroxide, t-butyl hydroperoxide, diacetyl peroxide and dibenzoyl peroxide are examples of the peroxy compounds disclosed. Alkoxysilanes and allyl chloride are included in the list of compounds useful in the invention. 0.05-10 weight percent, preferably 0.1-1 weight percent of the total weight of reactants is disclosed as the effective use range of the peroxides and hydroperoxides in the invention.
U.S. Pat. No. 4,061,609 discloses the advantageous use of hydroperoxides as temporary catalyst inhibitors in silicone rubber compositions cured via platinum-catalyzed hydrosilylation. On the other hand, U.S. Pat. No. 5,986,122 discloses that peroxides and hydroperoxides can inhibit hydrosilylations and claims the use of ascorbic acid and its derivatives to destroy peroxy compounds in allyl polyethers prior to hydrosilylation. Similarly, U.S. Pat. No. 5,103,033 discloses essentially oxygen-free conditions for the hydrosilylation synthesis of β-cyanoalkylsilanes catalyzed by copper-amine complexes.
In summary, the prior art discloses the beneficial use of oxygen and peroxy compounds in some hydrosilylations, but generalizations covering the broad range of transition metal catalysts, unsaturated substrates, hydrido silicon compounds and peroxy compounds are not possible from the available information. In fact, there are hydrosilylations in which oxygen and peroxy compounds are disadvantageous and inhibitive. Ruthenium-containing compounds are known to catalyze hydrosilylations of unsaturated substrates by alkoxysilanes. However, rates and yields are inconsistent for the specific cases of allyl substrates (for example, allyl halides) and alkoxysilanes (for example, triethoxysilane and trimethoxysilane). So in spite of the extensive prior art information, there still exists a need for a reliably consistent ruthenium-catalyzed hydrosilylation process affording high reaction rates and high yields of haloalkylalkoxysilanes from the reaction of allyl halides and alkoxysilanes. The present invention is believed to be an answer to that need.